Various types of hearing prostheses provide persons with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural hearing loss. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Persons with certain forms of conductive hearing loss may benefit from hearing prostheses, such as acoustic hearing aids or vibration-based hearing aids. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sounds into the person's ear. Vibration-based hearing aids typically include a small microphone to detect sound, and a vibration mechanism to apply vibrations corresponding to the detected sound to a person's bone, thereby causing vibrations in the person's inner ear, thus bypassing the person's auditory canal and middle ear.
Persons with certain forms of sensorineural hearing loss may benefit from cochlear implants and/or auditory brainstem implants. For example, cochlear implants provide a person having sensorineural hearing loss with the ability to perceive sound by stimulating the person's auditory nerve via an electrode array implanted in the person's cochlea. In traditional cochlear implant systems, an external component of the cochlear implant detects sound waves, which are converted into a series of electrical stimulation signals delivered to the implant recipient's cochlea via the electrode array. Electrically stimulating auditory nerves in a cochlea with a cochlear implant enables persons with sensorineural hearing loss to perceive sound.
A traditional cochlear implant system includes an external speech processor unit worn on the body of a prosthesis recipient and a stimulator unit implanted in the mastoid bone of the recipient. In this traditional configuration, the external speech processor unit detects external sound and converts the detected sound into a coded signal through a suitable speech processing strategy. The coded signal is sent to the implanted stimulator unit via a transcutaneous link. The stimulator unit (i) processes the coded signal, (ii) generates a series of stimulation signals based on the coded signal, and (iii) applies the stimulation signals to the recipient's auditory nerve via electrodes.
In another example cochlear implant, the functionality of the external speech processor unit and the implanted stimulator unit are combined to create a totally implantable cochlear implant (TICI). The TICI system can be either a monolithic system containing all of the components within a single implant housing or a collection of implant housings coupled together. In operation, detected sound is processed by a speech processor in the TICI system, and stimulation signals are delivered to the recipient via the electrodes without the need for a transcutaneous transmission of signals between an external speech processor unit and an implanted stimulator unit as in the traditional cochlear implant configuration described previously.